1. Field of the Invention
This invention relates to a method and device for correcting a fuel injection quantity in a diesel engine, and more particularly to improvements in a method and a device for correcting a fuel injection quantity, being suitable for use in a diesel engine provided with an electromagnetic spill type fuel injection pump, wherein means is provided for correcting a shift in phase of an engine rotation pulse and a dispersion in responses of an electromagnetic spill valve, whereby a control signal to the fuel injection pump is corrected in response to an output from the correcting means.
2. Description of the Prior Art
Along with the development in the electronic control techniques, particularly, the digital control technique in recent years, there has been commercialized the so-called electronic control diesel engine, wherein a fuel injection pump of the diesel engine is electronically controlled.
There are various methods of electronically controlling the fuel injection pump. One of the fuel injection pumps is a so-called electromagnetic spill type fuel injection pump, wherein fuel spill in the fuel injection pump is controlled by an electromagnetic spill valve. In this electromagnetic spill type fuel injection pump, when the fuel injection quantity reaches a target value, a spill port is opened by the electromagnetic spill valve to control the feed end of fuel, so that the fuel injection quantity per stroke can be controlled.
The electromagnetic spill valve is of a normally open type, for example, and on-off controlled by an electronic control unit (hereinafter referred to as an "ECU"), with a spill command angle theta obtained from an accelerator opening, an engine speed and the like, and as referenced from the position of an engine rotation pulse (hereinafter referred to as an "NE pulse"). In this case, as disclosed in U.S. Pat. Nos. 4,413,508 and 4,450,528 or Japanese Patent Laid-open No. 134377/1984, a phase correction resistor (hereinafter referred to as a "theta correction resistor") and a response correction resistor (hereinafter referred to as a "tau correction resistor") for correcting the shift in phase of the NE pulse and the dispersion in response of the electromagnetic spill valve are mounted on the fuel injection pump, for example. Both of the theta correction resistor and the tau correction resistor are adjusted in the shipping stage so that the fuel injection pump can have a standard injection quantity per stroke in its characteristics.
In such case as described above, for example, the ECU calculates a timing TSPon on which the electromagnetic spill valve is turned off (spill is on) in accordance with a flow chart shown in FIG. 5 (related art). More specifically, first, in step 110, the spill command angle theta is calculated from the engine speed and the accelerator opening which have been detected. Subsequently, in Step 112, a phase correction value (hereinafter referred to as a "theta correction value") Vrp read in from the theta correction resistor through an analogue-digital conversion, for correcting a change in an injection quantity per stroke due to a press-in shift of an engine rotation pulser (hereinafter referred to as an "NE pulser") and a shift in position of an engine rotation sensor (hereinafter referred to as an "NE sensor") is added to the spill command angle theta so as to obtain a value theta+Vrp(.degree.CA), from which a reference NE pulse No. n (for example, n=2) is calculated and a surplus angle is converted into a time to provide TSPon'. Subsequently, in Step 114, calculations shown in the following formula are performed to obtain a time TSPon for turning the electromagnetic spill valve off. EQU TSPon.rarw.TSPon'+Vrt (1)
where Vrt is a response correction value (hereinafter referred to as a "tau correction value") read from the tau correction resistor through an analogue-digital conversion, for correcting a change in an injection quantity per stroke due to dispersion in delayed response of the electromagnetic spill valve.
Subsequently, due to an interrupt by NE pulse, the process enters an NE interrupt routine as shown in FIG. 6 (related art), and, in Step 210 thereof, judgment is made as to whether No. n of NE pulse reaches or not. When the result of judgement is positive, the rountine proceeds to Step 212, where Tspon, which has been calculated in the Step 114, is set in an output compare resistor for interrupt OCR, thus completing this routine.
Thus, as shown in FIG. 7 (related art), upon reaching of NE pulse No. n (=2), the electromagnetic spill valve, which has been turned on, is turned off after TSPon, and the spill is performed, whereby the fuel injection is stopped.
However, when the theta correction resistor and the tau correction resistor are disconnected or short-circuited to a plus voltage side of a battery, the theta correction value Vrp and the tau correction value Vrt become excessively large, whereby the fuel injection quantity becomes excessively large, so that the diesel smoke is produced in large quantity, and moreover, the exhaust temperature and the temperature in the combustion chamber are raised, thus possibly resulting in a damaged engine.
Furthermore, to the contrary, when the theta and the tau correction resistors are short-circuited to the earth, the correction values become excessively small, whereby the fuel injection quantity becomes excessively small, so that there is a possibility of the vehicle unabling to run.